Chapters 4-5 Flashcards
Atom
The smallest particle of an element that retains its identity in a chemical reaction
What 2 things did Democritus conclude about atoms
- They were indivisible
2. They were indestructible
Dalton’s atomic theory (4 points)
- All elements are composed of tiny indivisible particles called atoms
- Atoms of the same element are identical. The atoms of one element are different from those of any other element.
- Atoms of different elements can physically or chemically combine in whole-number ratios to form compounds.
- Chemical rxn’s occur when atoms are separated from each other, joined, or rearranged in a different combination. However, rxn’s NEVER change atoms of one element into atoms of another.
What instrument is used to observe individual atoms?
Scanning electron microscope
Electron
A negatively charged subatomic particle
Cathode ray
A stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure
Proton
Positively charged subatomic particle found in the nucleus
Neutron
Subatomic particle with no charge and a mass of 1 amu; found in the nucleus
Nucleus
The tiny, dense, central portion of an atom, composed of protons and neutrons
Relative mass of an electron (mass of proton = 1)
1/1840
Relative mass of proton
1
Relative mass of neutron (mass of proton = 1)
1
Thomson’s contribution
Through the cathode ray experiment, discovered that electrons exist in atoms of all elements and have a negative charge
Millikan’s contribution
Through the oil-drop experiment, calculated the quantity of an electron’s charge and its mass
4 ideas about matter and electric charges
- Atoms are electrically neutral
- Electric charges are carried by particles of matter
- Electric charges always exist in whole-number multiples of a single basic unit; there are no fractions of charges
- When a given number of negative particles combines with an equal number of positive particles, a neutral particle is formed
Goldstein’s contribution
Observed protons in a cathode-ray tube
Quark
Subnuclear particle that composes protons and neutrons
Plum-pudding model
An atom consists of electrons stuck in a lump of uniformly positive material
Rutherford’s contribution
Through the gold-foil experiment, discovered that the atom is mostly empty space, where the electrons dwell, with all of the positively charged particles located in the small, centralized nucleus
Atomic number
The number of protons in the nucleus of an atom of an element
Mass number
The total number of protons and neutrons in the nucleus
Isotopes
Atoms of the same element that differ in their number of neutrons (same atomic number, diff. mass number)
Atomic mass unit (amu)
A unit of mass equal to 1/12 the mass of a carbon-12 atom
Atomic mass
The weighted average of the masses of the isotopes of an element
Elements are different because they contain different numbers of ________.
Protons
How to calculate the number of neutrons in an atom
Mass number - atomic number
What does the 197 signify in gold-197?
Gold’s mass number
How to calculate atomic mass of an element
Multiply the mass of each isotope by its natural abundance, expressed as a decimal, then add the products
Energy level
The specific energies an electron in an atom or other system can have
Quantum
The amount of energy needed to move an electron from one energy level to another
Atomic orbital
A mathematical expression describing the probability of finding an electron at various locations
What did Bohr propose in the Bohr model?
An electron is only found in specific orbits around the nucleus
What does the quantum mechanical model determine about electrons?
Determines the allowed energies an electron can have and how likely it is to find the electron in various places around the atom
Sublevels in principle energy level 1
1s (1 orbital)
Sub levels in principle energy level 2
2s (1 orbital), 2p (3 orbitals)
Sub levels in principle energy level 3
3s (1 orbital), 3p (3 orbitals), 3d (5 orbitals)
Sub levels in principle energy level 4
4s (1 orbital), 4p (3 orbitals), 4d (5 orbitals), 4f (7 orbitals)
Aufbau principle
Electrons occupy the lowest energy levels first
Pauli exclusion principle
An orbital may describe at most 2 electrons, each w/opposite spin direction
Hund’s rule
Electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible
